The Bernie Sanders campaign was not happy after the Human Rights Campaign, the nation’s largest LGBT rights group, endorsed Hillary Clinton for the Democratic presidential nomination Tuesday. A representative for the Vermont senator criticized the group, saying its endorsement “cannot possibly be based on the facts and the record,” the Washington Blade reported.

“It’s understandable and consistent with the establishment organizations voting for the establishment candidate, but it’s an endorsement that cannot possibly be based on the facts and the record,” Sanders spokesman Michael Briggs said.

Although the Human Rights Campaign endorsed then-Sen. Barack Obama in 2008 after he won the Democratic nomination, this time the group said in its endorsement of Clinton that they believe she is the strongest candidate to fight for their cause in November.

“All the progress we have made as a nation on LGBT equality — and all the progress we have yet to make — is at stake in November. In most states, LGBT people are still at risk of being fired, evicted or denied services simply because of who they are,” HRC President Chad Griffin said in a statement. “Today, 63 percent of LGBT Americans report having experienced such discrimination, and we are seeing other troubling trends, from the onslaught of state and local anti-LGBT measures to the national scourge of anti-transgender violence to backsliding on HIV/AIDS prevention and youth homelessness.”

The Democratic race has been heating up in recent days as Sanders has risen in both national and early state polls, eating away at Clinton’s lead and making her campaign nervous about its chances in Iowa and New Hampshire. Both candidates were throwing out sharp attacks during the Democratic debate Sunday night, clashing over guns, healthcare and Wall Street influence.

But support for lesbian, gay, bisexual and trans rights can be a particularly touchy issue for Clinton. The Don’t Ask Don’t Tell policy that barred openly gay people from serving in the U.S. military and the Defense of Marriage Act, which defined marriage as between one man and one woman, both became law under her husband’s administration. Clinton herself supported DOMA through her 2000 campaign for Senate in New York, and while she backed away from the law during her 2008 run for president, she did not announce her support for same-sex marriage until 2013.

In his comments Tuesday, Briggs touted Sanders as “somebody who’s been for gay rights long, long ago,” according to the Washington Blade, an LGBT publication. Sanders has long opposed anti-gay laws, signing a Gay Pride Day proclamation in 1983 when he was mayor of Burlington, Vermont.

Sanders was also one of 67 members of the House of Representatives to vote against DOMA in 1996, he opposed Don’t Ask Don’t Tell in 1993 and supported civil unions in Vermont in 2000, Time reported. But he too, like Obama and Clinton, "evolved" on same-sex marriage over time. He typically opposed bans on the issue, but did not speak out in favor of it until 2009, according to Time.

Briggs, the Sanders spokesman, recalled Clinton’s evolving record on same-sex marriage when commenting on her Human Rights Campaign endorsement.

“So who knows what prompted the Human Rights Campaign to do what it does — I have trouble myself figuring why they do some of the things they do over the years — but I think the gay men and lesbians all over the country will know who has been their champion for a long, long time and will consider that as they make up their mind on support for his campaign,” Briggs said.

Sanders’ campaign is not alone in questioning the Human Rights Campaign endorsement of Clinton. While the group fights for LGBT rights in many arenas, it has been criticized by many in the LGBT community for aligning itself with large corporations that don’t always have the most gay-friendly policies or are objectionable on other issues, for not being inclusive of transgender people and for a general lack of diversity.

On social media Tuesday, some people responded to the news of the Clinton endorsement by pointing out her mixed record on LGBT issues or by criticizing HRC itself.

Still, the Human Rights Campaign, which often goes by the initials it shares with the former secretary of state, recognized that all three Democratic presidential candidates support their causes and used the occasion of its endorsement to draw a contrast with Republicans. The group sent questionnaires to each presidential candidate asking about their support for various issues the organization cares about. All three Democratic candidates responded affirmatively to every action listed on the questionnaires, while no Republican candidate even returned the survey.

“There are certainly several friends of equality in this race, but the 32 community leaders who comprise HRC’s board of directors have unanimously decided that Hillary Clinton is the champion we need to fight for us each day on the campaign trail and every day in the White House,” HRC spokesman Brandon Lorenz said in a statement to the Washington Blade in response to the Sanders campaign’s remarks. “She has a strong record, a strong agenda, and a strong ability to win against any Republican running on an anti-LGBT platform in November and lead from Day One.”